code: def Send(self, request, context):
      client_id = request.client_id
      self.last_heartbeat_time = time.time()
      self.last_heartbeat_table[client_id] = time.time()
      return heartbeat_pb2.Reply(tag=remote_constants.HEARTBEAT_TAG)
  
imports: import grpc
  import os
  import time
  import threading
  from concurrent import futures
  from parl.remote import remote_constants
  from parl.remote.grpc_heartbeat import heartbeat_pb2
  from parl.remote.grpc_heartbeat import heartbeat_pb2_grpc
  from parl.utils import logger, get_ip_address
  import psutil
  import multiprocessing
label_desc: Use image node_id 2 for calling the GrpcHeartbeatServer obj's underlying member method code with example usage: obj.Send(request, context) and returns: heartbeat_pb2